Molecular Dynamics Simulations Of Diffusion For Al-Cu System

Diffusion is a dynamic procedure and plays a significant rule in various physical and chemical reaction processes, such as the oxidation of metals, sintering, carburizing, homogenizing and formation of semiconductor PN junction; all of these processes are closely bound up with diffusion. Both of aluminum and copper are widely used in the electronic industry, and the aluminum-copper composite structures also has a widely application in the filed of aerospace and microelectronics. The study of aluminum-copper joints is the key point of achieving availability of aluminum-copper composite structures. The study of the self diffusion of aluminum, copper and the diffusion of Al-Cu alloys are very important for joint of Al and Cu. In this paper, the molecular dynamics (MD) technique was employed to simulate the processes of self-diffusion of aluminum and copper and the diffusion bonding of Al/Cu interface in combine with the embedded atomic method (EAM) potential.For bulk diffusion, molecular simulation is confronted with a certain difficulty, e.g. at low temperatures, the atomic jump frequency is too low to produce the statistically significant atomic displacement within a short time and beyond the acceptable time scale of the molecular simulation. In this paper, the method of excess point defects created in the bulk was used to overcome the shortcoming of MD for diffusion. The linear expansion coefficient, vacancy formation and self-diffusion migration energy of Al and Cu were calculated. Then the self-diffusion activation energy was obtained by correction of the equilibrium defect concentration. The simulated results indicate that the method of excess point defects is suitable for molecular dynamics simulation of bulk diffusion.For the interface diffusion, the interface results in the interfacial atoms with a high jump frequency and rapid diffusion. The molecular dynamics simulator, hence, can be straightforward and visualized to simulate the process of diffusion. In this paper, aim to investigating the influence of temperature on diffusion bonding of Al-Cu interface and leave out the effect of pressure, a series of simulations were carried out by molecular dynamics technique. The present results show that the Cu atoms predominantly diffuse into A1side in the process of diffusion bonding and the thickness of the interfacial region depends on temperature. Higher temperatures lead to larger thicknesses. In the course of diffusion bonding, the interfacial region became disordered, in addition, the Cu atoms diffuses at low ratios but can deeply diffuses into the interior of Al and the Al atoms diffuses at a high ratios but hardly diffuses into the interior of Cu. Furthermore, the diffusion coefficient and activation energy of Al and Cu atoms were also calculated. The calculations indicate that the suitable temperature range for diffusion bonding of Al/Cu interface is750-800K. Finally, the diffusion mechanism of copper atoms in aluminum was analyzed. The main diffusion mechanism is nearest neighbor hopping.